1. Field of the Invention
The present invention relates to an ignition timing control apparatus and an ignition timing control method for an internal combustion engine, and particularly to a technique of controlling ignition timing according to a result of comparison between a magnitude (intensity) of vibration of an internal combustion engine and a determination value.
2. Description of the Background Art
Conventionally, various methods of determining whether knocking (knock) is present or absent have been proposed. For example, there is a technique of determining whether a magnitude of vibration detected in an internal combustion engine is larger than a determination value or not, and thereby determining whether knocking has occurred or not. However, the magnitude of vibration detected in the internal combustion engine may change due to secular changes in the internal combustion engine and a knock sensor. Also, the magnitude of vibration detected in a certain internal combustion engine may be different from those of other internal combustion engines. For precisely determining the presence/absence of the knocking, therefore, it is desired to correct the knock determination value according to the magnitude that is actually detected in the internal combustion engine.
Japanese Patent Laying-Open No. 2007-255195 has disclosed an ignition timing control apparatus for an internal combustion engine, including a detecting unit for detecting for a plurality of times a magnitude of vibration occurring in an internal combustion engine; a first calculating unit for calculating a knock magnitude related to a magnitude of vibration due to knocking, in accordance with each magnitude detected by the detecting unit; a controlling unit for controlling ignition timing of the internal combustion engine, based on a result of comparison between the knock magnitude and a predetermined first determination value; a second calculating unit for calculating a median value and a standard deviation of the magnitudes detected by the detecting unit; and a second correcting unit for correcting the first determination value so that a degree of ignition timing being retarded by the controlling unit becomes greater when a second determination value calculated by adding a product of the standard deviation and a predetermined coefficient to the median value is greater than the first determination value. The knock magnitude is calculated by dividing the magnitude of vibration by a BGL (Back Ground Level). The BGL is calculated by subtracting the product of the standard deviation and the coefficient from the median value.
According to the ignition timing control apparatus disclosed in the above publication detects multiple times the magnitude of the vibration occurring in the internal combustion engine. The knock magnitude related to the magnitude of the vibration that is caused by knocking is calculated according to each magnitude thus detected. The ignition timing of the internal combustion engine is controlled based on a result of the comparison between this knock magnitude and the predetermined determination value. For example, when the knock magnitude is larger than the determination value, the ignition timing is retarded. When the knock magnitude is smaller than the determination value, the ignition timing is advanced. When the second determination value calculated by adding the product of the standard deviation and the predetermined coefficient to the median value is larger than the first determination value, the first determination value is corrected and increased by an extent to which the control unit retards the ignition timing. Thereby, in a state where the knocking occurs frequently, it is possible to suppress excessive increase of the determination value to be compared with the magnitude of vibration with respect to the vibration occurring in the internal combustion engine. Therefore, the ignition timing can be retarded easily. Consequently, occurrence of the knocking can be suppressed.
When the load of the internal combustion engine suddenly changes, sudden changes necessarily occur in magnitude of the vibration. Thereby, the standard deviation of the magnitude may increase suddenly. Therefore, in the case where the knock magnitude is calculated according to the standard deviation of the magnitude, as is done in the ignition timing control apparatus disclosed in Japanese Patent Laying-Open No. 2007-255195, the knock magnitude may suddenly increase at the time of change of load the internal combustion engine even when the knocking has not occurred. In this case, the ignition timing is erroneously retarded.